Hydrocarbon conversion



Patented July 1947 umrao sures um, OFFICE L V Hillis O. Folkins, Skokie, 11L, alsignor to The Pure OilCompany, Chicago, Ill, a corporation Application August 9, 1944QSerlal No. 548,672

This invention relates to conversion of hydrocarbons and is more particularly concerned with a method for converting higher boiling hydro carbons into lower boiling hydrocarbons and for making unsaturated hydrocarbons from saturated hydrocarbons.

I have discovered that if thermal conversion of hydrocarbons is carried out in the presence of a ll amount of oxygen admixed with a small amount of bromine or iodine, or both, the cracking of the hydrocarbon is greatly accelerated so that it is possible to obtain larger yields of cracked hydrocarbons under the same timetemperature-pressure conditions than it is possible to obtain in thermal cracking of the hydrocarbons without sensitizer, and it'is' possible to obtain yields at lower temperatures which are commensurate with yields obtainable at higher temperatures without sensitizers. The invention is applicable to either batch or continuous meth- 6 Claims. (Cl. 196-52) them to the reaction zone or they may be injected directly into the reaction zone. sitizer mixture may be used in concentrations from approximately .055 mole percent to 5 mole percentbased on the total charge and should contain not less than about .005 mole percent of bromine and/or iodine, and not less than about .05 mole percent of oxygen. Higher concentrations of sensitizers may be used, but within the limits above set forth the reaction progresses rapidly without causing accumulation of undesirably large amounts of the sensitizers and their ods of cracking. In continuous cracking methods by operating under usual thermal cracking conditions in the presence of the oxygen-bromine sensitizer, not only can increased yields be obtained but higher octane gasoline can be pro-' duced. By using the sensitizer, a larger throughput of charging stock through a given size unit can be efiected because of the acceleration in the cracking reaction caused by the sensitizer.

An object of the invention is to provide a method for conversion of hydrocarbons.

Another object of the invention is to provide a method for accelerating cracking of hydrocarbons.

Still another object of the invention is to provide a method for increasing octane number of motor fuel made by cracking of hydrocarbons.'

A further object of the invention is to provide a sensitizer which will accelerate the decomposition of hydrocarbons.

A still further object of the invention is to provide a method for improving thermal cracking of hydrocarbons.

. Other objects of the invention will become apparent from the following description and the accompanying drawing, of which the single figure is a graphical representation of data showing the unexpected results obtained under certain conditions using sensitizers in accordance with our invention.

In accordance with the invention, a small amount of oxygen and bromine and/or iodine is mixed with the hydrocarbons subjected to decomposition. The oxygen and the halogen may be mixed with the hydrocarbons prior to charging decomposition products in the motor fuel or other product which it is desired to produce. In the experimental work I have found that a mixture containing from .03 to 2 mole percent of bromine and/or iodine and from .25 to 2 mole percent of oxygen gives unusually good results.

The invention is useful in conjunction with conventional types of thermal cracking in which the hydrocarbons are cracked at temperatures within the range of approximately 375 C. to 750 C. and is applicable to conversion of hydrocarbon gases such as propane and butane as well as to the conversion of liquid hydrocarbons such as heavy naphtha, kerosene and gas oil. The combination of the bromine and/or iodine with oxygen accelerates the cracking reaction to an extent far in excess of that which would be expected from the additive effect of 'the oxygen and the bromine or iodine alone. In order to demonstrate this fact a number of runs were made using norv mal butane as charging stock. The butane had a purity of 99%. The runs were all made in a Pyrex glass reaction vessel at temperatures either of 500 C. or 525 C. Before starting each run the reaction vessel was heated to the desired re-' action temperature and then evacuated by means of a vacuum pump to a pressure below 0.001 mm. of mercury. Sufiicient butane in admixture with the desired amount of sensitizer composition was then charged to the evacuated vessel until the pressure in the vessel approximated atmospheric pressure. The reaction was permitted to proceed in the closed reaction vessel while the temperature was maintained either at 500 or 525 C. until a pressure increase of 25 percent above the initial pressure was observed, whereupon the reaction gases were rapidly removed from the reactor and analyzed. In some runs where the ac celeration in reaction was extremely rapid the pressure increase somewhat exceeded 25 percent before the reaction was terminated.

A number of runs were also made without any The total sen-' sensitizer and other runs were made using only oxygen and only bromine as aensitizer.

Data for runs made at 525 C. are tabulated in Table I. lamb of the runs the initial pressure bromine or oxygen alone. In order to demonstrate that the increase in acceleration of reaction when using a combination of bromine and oxygen is greater than the cumulative effect of was calculated, a pressure reading was made 0.5 5 the two sensitlzers, curves were plotted for runs minute after the run began, thereafter pressure 694-3, 648-3, 687-3 and the average of readings were made at intervals of 1 minute from runs 679-3, 684-3, 692-3, 693-3 and 698-3. As the beginning of the run until 6 minutes thereshown in the drawing, the curves are plotted as after, from that point readings were made at 2 time in minutes as abscissae and pressure in.

minute intervals until 20 minutes after the run 10 crease as ordinates. began, and when it was necessary to run in ex- Referring to the drawing, curve 1 is plotted cess of minutes to obtain pressure infrom the averages of the time and pressure readcrease, readings were taken at 5 minute intervals ings of the aforesaid blank runs. Curve 2 is plotduring the period from 20 to minutes and at ted from the time and pressure readings recorded 10 minute intervals beyond 40 minutes until the 15 in run 694-3 in which .25 mol percent of oxygen end of the run. The figures appearing in the was used as sensitizer. Curve 3 is plotted from table for 5% and 12.5% pressure increases were the time and pressure readings recorded in run obtained from curves representing pressure in- 648-3 in which .5 mol percent oi. bromine was creases plotted against time recorded in the runs used as sensitizer. Curve 4 represents the hypoindicated. In the table the figures given under 20 thetical or cumulative results which would be exthe heading Time in minutes for AP of 25% are pected from using together .5 mol percent of in some cases recorded and in other cases are bromine and .25 mol percent of oxygen. Curve 4 interpolated from curves based on recorded presis obtained by adding at any selected time (from sures because in certain runs the pressure rose curve 1) the pressure increase caused at the same above 25% increase too rapidly to obtain a read- 25 time by the presence of oxygen alone (curve 2 ing at the exact point. minus curve 1) and the pressure increase caused Tsar-a v N-butane decomposition at 525 C.

5...... 4.... 11111151 M... Run No. Cm. Hg Calsensitize! swab Per cent eulated Res.

5% 12.5% 25% 5% 12.5% 25% Acids Unsats. 00 H:

} 10.22 N 2.01 7.83 21.11 0.0 22.1 0.1 1.5 15.4 10.05 Oxygen.-- 0.5 0.10 4.10 16.98 20.1 1.0 1.3 0.2 2.5 0.5 2.2 14.5 15.15 ro 0.5 0.31 1.12 3.42 1.0 1.3 5.5 0.0 23.5 0.2 0.0 15.4 7345 Bromina--- 0.5 0.05 0.20 1.10 41.4 30.2 12.5 0.2 21.1 0.4 1.2 11.1

Oxygen---" 0.5 51.10 Bromine-- 0.25 0.30 1.53 4.50 5.1 5.3 5.0 0.0 23.3 0.3 1.1 15.3 10.35 Oxygen"-.- 0.25 0.50 5.01 10.10 3.5 1.3 1.1 0.0 23.4 0.1 1.0 14.0 mm 3 15 1 150 0 22 0.05 0.20 2.50 41.4 30.2 0.1 0.1 23.0 0.2 1.2 15.5 BrominIIII 0111 '0'65' "'0125 "'2T65' 'iiil' 'if' ""013 "25.1' "6.1' "it "22:2 Oxygen 0.25

! igti t B terminated at 31.05% pressure increase.

I Ran 687-3 terminated at 29.5% pressure increase.

The sensitization factors recorded in the table are obtained by dividing the time required for a particular pressure increase without sensitizer by the time required for the same pressure increase with sensitizer. Five blank runs, namely,

' 679-3, 684-3, 692-3, 693-3 and 698-3 were made in order to form a basis of comparison with the sensitized runs and the averages for the blank runs were used in calculating sensitization factors.

3y reference to the table it will be seen that oxygen greatly accelerates the reaction in its initial stages, but rapidly .loses its ability to continue to sensitize the reaction. For example in run 681-3, a 5 percent pressureincrease was obtained, 20.? times faster than without a sensitizer; whereas, a 25 percent pressure increase was obtained only 1.3 times faster than without sensitizer. On the other hand, the sensitization produced by bromine is relatively constant during the reaction. In run 648-3 the sensitization factor dropped only from 7 to 6.6 and in run 649-3 the sensitization factor dropped only from at the same time by the presence of bromine alone (curve 3 minus curve 1) and plotting on the graph the figures obtained for a 'suflicient number of different time periods to be able to draw a curve through the points; For example, at 8 minutes after the run began, the pressure increase without any sensitizer was 6.45 percent (obtained from curve 1) After the same period of time, the pressure increase for oxygen alone was 9.05 percent (obtained from curve 2) and the pressure increase for bromine alone was 22.8 percent (obtained from curve 3). The pressure increase, due to the presence of oxygen, is therefore 9.05 minus 6.45 or 2.6 percent. The pressure increase, due to the presence of bromine alone, is 22.8 minus 6.45 or 16.35 percent. The pressure increase that might be expected from the combination of .25 mol percent of oxygen and .5 mol percent of bromine for 3 minutes of running time is the sum of the pressure increase at that time without sensitizer and the pressure increases caused by each of the sensitizers, or 6.45 plus 2.6 plus 16.35 or 25.4 percent pressure increase. 3y referring to curve 4, it will be seen that a pressure increase of 25.4 percent is obtained after 3 mintained in run 687-3 using .25 mol percent or oxygen and .5 mol percent or bromine as sensitizers. Instead of requiring three minutes to obtain a pressure increase of 25.4 percent, as indicated from the additive result, only 2.1 minutes were required to obtain'the same pressure increase, thus, showing that the acceleration was considerably greater than would be expected from the results on the individual sensitizers.

It will be apparent from the analysis of the products in the table that the reaction is primarily one of splitting of a carbon to carbon bond as shown by the relatively large amount of unsaturated hydrocarbons and the low amount of hydrogen formed in the reaction. The nature of the reaction products is essentially the same with or without sensitizer.

The invention is useful in connection with known types of mineral oil thermal cracking without catalyst. It is also useful in catalytic cracking operations wherein a known solid comminuted catalyst, such as natural or synthetic alumina-silica compositions. is used. The invention may be used in connection with cracking of gases to make unsaturated hydrocarbons, such as cracking of propane to ethylene, cracking of butane to ethylene and propylene or the cracking respectively, and the maximum combined amount 01' oxygen and halogen in the mixture being about5 mole per cent.

2. Method in accordance with claim 1 in which the halogen is bromine.

3. The method of cracking hydrocarbons having at least 3 carbon atoms in the molecule which consists in heating said hydrocarbons to a temperature of approximately 375 C. to 750 C. in the presence simultaneously of a mixture of oxygen and bromine. the oxygen being present in the total mixture undergoing conversion in an amount not less than about .05 mole percent,

REFERENCES CITED The following references are or record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,250,879 Hirt Dec. 18, 1917 1,925,421 Van Peski Sept. 5. 1933 2,213,345 Marschner Sept. 3, 1940 2,275,232 Rice Mar. 3, 1942 2,351,793

Voorhees June 20, 194 

